Functional neuromuscular stimulation system

ABSTRACT

An input command controller (A) provides logic function selection signals and proportional signals. The signals are generated by movement of a ball member (12) and socket member (14) relative to two orthogonal axes. When the joystick is implanted, a transmitter (50) transmits the signals to a patient carried unit (B). The patient carried unit includes an amplitude modulation algorithm such as a look-up table (124), a pulse width modulation algorithm (132), and an interpulse interval modulation algorithm (128). The algorithms derive corresponding stimulus pulse train parameters from the proportional signal which parameters are transmitted to an implanted unit (D). The implanted unit has a power supply (302) that is powered by the carrier frequency of the transmitted signal and stimulation pulse train parameter decoders (314, 316, 318). An output unit (320) assembles pulse trains with the decoded parameters for application to implanted electrodes (E). A laboratory system (C) is periodically connected with the patient carried unit to measure for changes in patient performance and response and reprogram the algorithm accordingly. The laboratory system also performs initial examination, set up, and other functions.

This application is a continuation of U.S. application Ser. No.08/474,928, filed on Jun. 7, 1995, which is a divisional of U.S.application Ser. No. 08/301,268 filed Sep. 6, 1994, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to the art of functional neuromuscularstimulation. It finds particular application in providing hand controlfunctions in central nervous system (CNS) disabilities such asquadraplegia and stroke victims and will be described with particularreference thereto. However, it is to be appreciated that the inventionis also applicable to providing locomotive and control of other lowerbody functions in CNS disabled victims and to providing control of othermuscles over which the patient has lost partial or full voluntarycontrol.

In healthy humans, electrical signals originate in the brain and travelthrough the spinal cord and subsequently to peripheral nerves to amuscle which is to be contracted. More accurately, the signals travel totwo or more muscles whose contractions apply forces antagonistically toa joint structure. The relative forces determine the degree and speed ofmovement. By appropriately applying the electrical stimulation tovarious muscles, a wide degree of voluntary movement can be achieved. Ininjuries to the CNS, the passage of electrical signals through theinjured area may be disrupted. Commonly, lower spinal cord injuries willterminate the transmission of electrical control signals to muscles inthe lower part of the body. Damage to the upper part of the spinal cordmay block the flow of voluntary muscular control signals to upper andlower body regions. For example, in an upper spinal column injury at theC6 vertebrae, which is frequently injured in accident victims, muscularcontrol below the elbows is commonly lost.

As early as 1791, Luigi Galvani produced artifical contractions in themuscle of frogs' legs by the application of electrical potentials. Inthe ensuing years, electrical stimulation therapy has been greatlyrefined. Cardiac pacemakers, for example, have become commonplace.

Several different groups of researchers have enabled paraplegic patientsto stand and walk with walkers or crutches by applying preselectedsequences to surface electrodes over their leg muscles. Surfacestimulation is satisfactory for some walking and other less detailedmovements. However, with surface electrodes, it is difficult to make anaccurate selection of the muscle to be stimulated or an accurateprediction of the strength of the stimulus signal reaching the muscle.

Surgically implanted electrodes provide accurate selection of the muscleto be stimulated. Further, the stimulation remains more consistent overa long period of time. This renders implanted electrodes advantageousfor the more delicate and complex motion associated with the hands.

Numerous experimental systems have been devised and implemented toprovide computer controlled electrical stimulation to the muscles of thelegs, arms, and hands of patients. These experimental systems arecommonly large and bulky. Frequently, the patient must be connected witha personal computer or other small computer by a cable or tether.Although smaller, dedicated computer systems could be designed, thelarger programmable computer systems are generally preferred forexperimental flexibility. The response to a given stimulus varies widelyamong patients and over time within each patient. The largerprogrammable computer facilitates customizing for different patients andchanges in a given patient.

The present invention provides a new and improved functionalneuromuscular stimulation system which increases patient independenceand performance.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a functionalneuromuscular stimulation system is provided. An input command meansprovides a command control signal which is indicative of a selectedphysiological movement or group of movements. A first parameterprocessing means derives the parameters of a first stimulus pulse trainfrom the control signal. The first parameter processing means includesan amplitude means for selecting an amplitude of each stimulation pulseof the pulse train, an interval means selects an interpulse intervalbetween pulses of the pulse train and a pulse width means selects apulse width for each pulse of the pulse train, each in accordance withthe control signal. A pulse train generator generates a pulse train withthe selected amplitude, interpulse interval, and pulse width. Anelectrode is connected with the pulse train generator for applying thepulse train to a muscle to be stimulated.

In accordance with a more limited aspect of the present invention, aplurality of similar parameter processing means are provided foruniquely deriving additional stimulation of pulse trains from thecontrol signal(s) for application to additional electrodes implanted atother locations in the same or other muscles.

In accordance with another more limited aspect of the present invention,a physiological parameter monitor is provided for monitoring apreselected parameter of physiological movement, such as position orforce. A parameter comparing means compares the monitored parameter witha parameter value retrieved from a preprogrammed look-up table. Anydifference between the monitored and retrieved parameters is determined.At least one of the amplitude, interpulse interval, and the pulse widthof the stimulus pulse train are adjusted such that the difference isminimized.

In accordance with another aspect of the present invention, aHall-effect command control signal generator is provided. A permanentmagnet is mounted in a ball member, such as in an externally worn deviceor surgically implanted, e.g. in the clavical of the patient. A firstpair of Hall-effect plates are mounted in a socket member, such asexternal device or the sternum of the patient to define an axis. Atleast one additional Hall-effect plate is mounted in the socket memberto define a second axis. A power supply provides a current flow in onedirection across each of the Hall-effect plates. A potential differencemonitoring means monitors the potential difference generally transverseto the first direction across each Hall-effect plate to provide anoutput signal indicative of the change of potential thereacross. In thismanner, as the permanent magnet moves relative to the Hall-effectplates, the change in their relative proximity causing correspondingchanges in the magnetic flux density across each plate which causescorresponding changes in the path of current flow along said onedirection, hence the potential difference across the Hall-effect plates.In this manner, the output signals from the potential differencemonitoring means are indicative of the angular position of the ball andsocket member relative to the first and second axes.

In accordance with another aspect of the invention, a joystick includesa ferrite core mounted in a ball member. The ball member is rotatablymounted in a socket member. A driving coil is connected with the socketmember encircling at least a portion of the ferrite core. A plurality ofsensing coils are mounted to the socket member adjacent the ferrite coresuch that the transfer of an input signal from the driving coil to eachof the sensing coils is controlled by the relative proximity between theferrite core and the sensing coils.

In accordance with another aspect of the invention an implantedtelemetry system is provided. An antenna receives a radio frequencysignal which is converted into electromotive power by a power supply. Anencoding means encodes an electrical signal which controls a gate means.The gate means selectively connects a load across the antenna tomodulate a characteristic thereof such that a monitorable characteristicof the radio frequency signal is also modulated by the load.

In accordance with another aspect of the present invention, a laboratorysystem customizes electrical stimulus pulses to the patient. The systemincludes a command processing means for providing control parametersindicative of selected command functions and degrees of movement. Amovement planning means derives movement parameters indicative ofpreselected movement, force, or other motion related parameters of thecontrolled limb in response to each control parameter. A coordinationand regulation means derives appropriate stimulus parameters from themotion parameters. A stimulus generator assembles an appropriateelectrical stimulus pulse train in accordance with the stimulusparameters.

In accordance with a more limited aspect of the present invention, acomparing means is provided for comparing actual physical motionparameters achieved by the patient's limb being controlled and theselected motion parameters of the movement planning means. The stimulusparameters selected by the coordination regulation means areautomatically adjusted in order to bring the actual and selected motionparameters into optimal coincidence.

In accordance with another aspect of the present invention, amultichannel implanted stimulator system is provided. The stimulatorsystem includes an antenna for receiving a carrier signal which ismodulated with channel, pulse width, and pulse amplitude information forone or more of the channels. A power supply means derives operatingvoltage for other system components from the carrier signal. A decodingmeans decodes at least selected channel, pulse width, and pulseamplitude information from the modulations. For each channel, an energystorage means is provided for providing energy for a current pulse fromthe power supply through the muscle tissue between a stimulatingelectrode and a reference electrode. A channel selection means selectsthe appropriate channel and corresponding stimulating electrode to whichan electrical pulse of the decoded pulse width is to applied. A currentregulating means regulates the amplitude of the pulse in accordance withthe decoded amplitude.

In accordance with another aspect of the invention, the implantedstimulus system includes a metal capsule which defines a hermeticallysealed chamber therein. A receiving antenna receives signals indicativeof the stimuli to be applied to electrodes. Electrical circuitry ismounted in the capsule for converting received radio frequency signalsinto stimulus pulses. A plurality of electrical leads are electricallyconnected with the circuitry and the electrodes and mechanicallyconnected with the capsule.

In accordance with another aspect of the invention, an electrical leadconstruction for implanted electrodes is provided. First and secondlengths of multi-strand wire are wrapped helically around a longitudinalaxis of the lead. A flexible polymeric insulator material encapsulatesthe helically wound wires.

In accordance with another aspect of the present invention, a shieldassembly is provided for protecting a percutaneous interface. A shieldmember includes a peripheral lip portion extending peripherally around acentral shield member portion. The central shield member portion isconstructed of a resilient elastomeric material with a low profile. Anaperture is defined through the central shield member for alignment witha point at which electrical wires pass through the patient's skin. Anelectrical connector which is operatively connected with the electricallead wires passing through the patient's skin is mounted to the shieldmember central section. An overlay member having an aperture whichconforms with the shield member central portion overlays the shieldmember and is adhesively adhered to the shield member peripheral lipportion and to the patient's skin around the shield member.

One advantage of the present invention is that it is readily customizedto an individual patient. Moreover, the customization can be altered andrefined as the patient becomes more proficient with the apparatus, asthe patient's muscles become stronger, and the like.

Another advantage of the present invention resides in its portability.

Yet, another advantage of the present invention resides in the ease withwhich operators can adapt it to an individual patient.

Still further advantages of the present invention will become apparentto those of ordinary skill in the art upon reading and understanding thefollowing detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various steps and arrangements of stepsand in various parts and arrangements of parts. The drawings are onlyfor purposes of illustrating a preferred embodiment of the invention andare not to be construed as limiting it.

FIG. 1 is a diagrammatic illustration of the present invention incombination with a user;

FIG. 2 is a block diagram of a functional neuromuscular stimulationsystem in accordance with the present invention;

FIG. 3 is a side sectional view of a Hall-effect joystick in accordancewith the present invention;

FIG. 4 is a view of the socket of FIG. 2 through section 4--4;

FIG. 5 is a circuit diagram of the Hall-effect joystick and atransmitter for transmitting joystick position information to thepatient exterior;

FIG. 6 is a block diagram of the interaction between a patient-carriedunit and a laboratory system;

FIG. 7 is a hardware diagram of a patient-carried microprocessor basecontrol unit of the stimulator system of FIG. 1;

FIG. 8 is a diagrammatic illustration of an exemplary muscle stimulationelectrical pulse sequence in accordance with the present invention;

FIG. 9 is a further block diagram of the patient-carried unit of FIG. 7;

FIG. 10 is diagrammatic illustration of thumb and finger extension,flextion, and force as a function a proportional command signal during astimulated thumb and forefinger gripping motion;

FIG. 11 is a diagrammatic illustration of the data handling stages ofthe laboratory system;

FIG. 12 is a hardware configuration of a laboratory system whichinterfaces with the patient-carried stimulator;

FIGS. 13, 14, and 15 are diagrams of data processing in the laboratorysystem of FIG. 12;

FIG. 16 is a diagrammatic illustration of an implanted stimulator forstimulating implanted electrodes;

FIG. 17 is a detailed diagram of the power supply of the implantedstimulator;

FIG. 18 is a detailed illustration of the circuitry for applyingelectrical pulses through muscle tissue between a stimulus and areference electrode;

FIG. 19 is a side sectional view of the implanted stimulatorillustrating the mechanical encapsulation thereof;

FIG. 20 illustrates electrode lead wire construction;

FIG. 21 is an expanded view of a lead wire connector;

FIG. 22 is a side sectional view of an alternate embodiment of ajoystick in accordance with the present invention;

FIG. 23 is a sectional view of the joystick of FIG. 22 taken throughsection 23--23; and,

FIG. 24 is an expanded, perspective view of a percutaneous interface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIGS. 1 and 2, an input command control means Aproduces electrical command control signals for controlling the limb ormuscles in question. The input commands are derived from remainingvoluntary functions of the patient, e.g. shoulder. In the preferredembodiment, the input control means provides both function selection orlogic signals and proportional signals in response to shoulder movementof the patient. The function selection signal selects the motor functionto be performed, such as turning the system on or off, freezing thestimulus parameters applied to the patient's hand, selecting among apreselected group of gripping or other hand motions, and the like. Theproportional signal indicates a selected degree of the physical movementor force. In this manner, the patient can accurately control theprogress of the selected movement, the position of the hand, arm orother limb, the strength of a grip, and the like.

A portable, patient-carried control system or means B receives thefunction selection and proportional signals from the input command meansA. From the received signals, the portable control system selects theappropriate electrodes to receive electrical stimulation and theappropriate electrical stimulation signals for each electrode. Morespecifically, the portable control means B selects the pulse width,interpulse interval, amplitude, or other characteristics of anelectrical stimulation signal or pulse train in accordance with theproportional signal. The portable system selects appropriate electrodes,algorithms or conversion factors between the proportional signal andstimulation signal parameters, internal control functions, and the likein response to the received function selection signals.

A central or laboratory reprogramming means or system C selectivelyreprograms the portable system B.

The reprogramming adjusts the relationship between the proportionalsignal and the electrical stimulus signals, alters the internal controlfunctions, and otherwise customizes the portable system to the patient.As the patient's muscle tone and strength improve with the continueduse, the operating parameters of the portable control system B arereprogrammed and refined. Further, the central means C analyzes theperformance of the portable system for potential failures or defects,accumulates and analyses historical data, provides physical therapyinstructions, derives data of therapeutic value to the operator,provides training routines, and the like.

In the preferred embodiment, the portable control means B only selectsthe appropriate electrical stimulation pulse train parameters. A firstimplanted stimulator means D under the control of the portable system Bapplies the electrical signals to first implanted electrodes E tocontrol a first body function, such as hand movement. A second implantedstimulator D' selectively receives control signals from the portablesystem B and applies electrical signals to one or more second implantedelectrodes E' to control a second body function, such as bladdercontrol. Additional implants may also be provided. Preferably, eachimplant has an interrogatable identification which is interrogated bythe portable unit B. The portable unit correlates the transmittingchannels with the corresponding implanted unit. This self correctingfeature saves the patient the inconvenience of matching a dedicatedtransmitting antenna with a specific implant. Alternately, the portablesystem may be connected directly with the electrodes E through apercutaneous interface.

With continuing reference to FIG. 1 and particular reference to FIGS. 3and 4, one of the preferred embodiments of the input command controlmeans A is provided. The input command control means is mounted to becontrolled by the shoulder of the patient opposite to the hand which isto be controlled. To control the right hand, the input control ismounted for movement by the left shoulder. A permanent magnet 10 isimbedded in a ball member, preferably surgically implanted in theclavical 12 of the patient. In a matching socket joint 14, preferably inthe sternum, four Hall-effect transducer plates 16, 18, 20, and 22 aresurgically mounted. Hall plates 16 and 20 are mounted along a first axiswhich is orthogonal to a second axis along which Hall elements 18 and 22are mounted. Preferably, the Hall elements are mounted in coordinationwith the axes along which the patient has the greatest, mostcontrollable shoulder motion. It is to be appreciated that other numbersof plates may be used. For example, three plates can define two axes.Even two plates can define the relative position of the ball member andsocket, but with an ambiguity. In some applications, proper placement ofthe plates and signal processing circuitry may be able to resolve theambiguity adequately.

With reference to FIG. 5, each Hall element is a conductive plate acrosswhich a current is induced flowing from a power regulator 24 to ground.In accordance with the Hall-effect, the current passing through theconductive plate is deviated toward the side of the plate in thepresence of magnetic flux from the permanent magnetic 10. This deviationcauses a change in the potential difference between the sides of theplate which is proportional to the magnetic flux density through theelement which, in turn, varies with the proximity of the permanentmagnetic 10 thereto. Differential amplifiers 26, 28, 30, and 32 are eachassociated with one of the Hall-effect plates to measure the potentialchange thereacross.

A first axis differential amplifier 34 differentially combines theoutput of differential amplifiers 26 and 30 to produce a first axisanalog signal which is proportional to motion of the permanent magneticrelative to the first axis. A second axis differential amplifier 36 isconnected with the Hall elements to provide a second axis analog outputsignal which varies in proportion to the position of the permanentmagnetic along the second axis.

In the preferred embodiment, the output signal from the Hall elementsalong the axis along which the patient has the greatest range ofmovement provides the proportional signal and the output signal fromalong the other axis provides the function selection or logic signal. Inthe preferred embodiment, the function is changed in response to thefunction selection signal making a sudden change in amplitude of atleast a preselected duration.

Optionally, an accelerometer may be mounted in the patient's shoulderand the output of the accelerometer may provide the function selectionsignal. Proportional control signals may then be provided correspondingto two axes. As yet another option, the Hall-effect elements and thepermanent magnet may be mounted in a ball and socket joint of man-madeconstruction. The two portions of the man-made ball and socket joint areselectively connected with portions of the shoulder, either externallyor implanted.

With continuing reference to FIG. 5, the power supply 24 is connectedwith a receiving antenna 40 which is irradiated with a radio frequencysignal applied external to the patient by a power transmitting cord 42of the portable unit B. The received signal, in the preferred embodimentabout 10 MHz., induces currents in receiving antenna 40 which areconverted to motive power by the power supply 24.

A telemetry unit 50 receives the first and second analog outputs of theHall-effect joystick for transmission to the portable processor B. Thetelemetry unit includes an encoding means 52 which encodes the firstaxis signal from amplifier 34 and the second axis signal from amplifier36 into a preselected digital format. Optionally, analog formats mayalso be implemented. The ones and zeroes of the encoded digital signalcontrol a gate means 54 which selectively applies a load 56 across thereceiving coil 40. The applied load changes the characteristics in amanner which can be sensed by the power transmitting coil 42 and theportable unit B. Alternately, the encoded signal from the telemetry unit50 may be transmitted on a carrier frequency for reception by areceiving coil of the portable unit B. As another alternative, directelectrical connection can be utilized, particularly if the joystick ismounted to the patient externally.

In a typical functional interactive system operation, electricalcommunication is established between the input command controller A andthe portable unit B. In the preferred embodiment, making this connectionfirst prevents the unit from going into the exercise mode. Second, anelectrical interconnection is established between the portable unit Band the implanted electrodes E. The system powers up to an idle modewhich is a non-stimulating low power consumption state.

In the preferred embodiment, the patient depresses a switch mountedadjacent to the shoulder position transducer to commence operation. Thesystem goes into a grasp mode selection scan in which feedback cuesindicate which grasp mode is indicated. Releasing the chest switch orperforming another preselected operation, such as shifting the shouldervertically, stops the scanning in the desired grasp mode.

During a short delay, the patient positions his shoulder forward and aftat a desired zero set point. The portable unit sets itself with theselected position as the zero or null set point between plus and minusranges of motion. It is to be appreciated that if the operator does notselect the center of his physical movement range, significantly greatercontrol will be provided in one direction of movement than in the other.After the set point selection delay, the system turns on in a functionalmode with the defined set point representing a zero level of command.Shoulder movement from the set point, in turn, proportionally controlsthe selected grasp.

Rapid movement along the axis orthogonal to the proportional axisinitiates a hold or lock mode which maintains a constant stimulus outputindependent of shoulder position. To exit the hold mode, another rapidmovement allows the user to regain proportional control after realigningthe shoulder to the position it was in along the proportional controlaxis when the hold was initiated. This provides a smooth transition fromthe hold mode to the proportional control mode without disrupting thegrasp. Feedback cues, such as audio tones, indicate the state ofoperation to the user. To place the system in idle mode, the userdepresses and releases the chest mounted switch.

With particular reference to FIG. 6, the signals from the input commandcontroller A are operated on by control algorithms 60 which operate onthe proportional signals with algorithms which select muscles to bestimulated and electrical pulse stimulation characterisitics for eachmuscle. A formating means 62 formats the stimulation pulse traincharacterisitics to an appropriate format to be transmitted by radiofrequency transmitter 64 to the implanted stimulator D. A portablepercutaneous stimulator 66 enables the formated control signals to beapplied directly to the electrodes E through a percutaneous interface68.

Referring again to FIG. 1, the patient-carried control B includes areceiver 70 for receiving the function selection and proportionalsignals, i.e. the first and second axis signals. When the input controlis externally mounted or when the interconnection is by way of apercutaneous interface, electrical wires directly connect the patientcarried control B and the input control means A. When the input controlmeans is implanted and the patient-carried control system is externallycarried, they are interconnected by the telemetric interface SO.

With reference to FIG. 7, a programmable gain and offset means 80selectively adjusts the gain and an offset for an analog proportionalsignal to bring it into the appropriate range for an analog to digitalconverter 82. The function selection signal is conveyed directly toselected channels of the analog to digital converter 82. With digitalreceived signals, the gain and offset means and the analog to digitalconverter are eliminated.

An feedback means 84 provides the patient with feedback regarding thestate of the portable unit, e.g. selected grapsing mode, on/off state,locking mode, the position of the null set point, or the like. Thefeedback means 84 may be a tone generator, an electrocutaneous systemsuch as a shoulder mounted electrodes 84 of FIG. 1, or the like. Theelectrocutaneous feedback is advantageous in public environments inwhich the audio tones may prove indiscernable or embarressing to theuser. Microprocessors 86 and 88 select electrical stimulation signalparameters in accordance with the input proportional and functionalselection signals and in accordance with patient parameters retrievedfrom memories 90, 92, 94, and 96. The microprocessors 86 and 88 areinterconnected by a processor bus to perform distributed processingoperations. This enables the microprocessors to share responsibility,handle high level math, accommodate additional microprocessors for moresophisticated control functions. Output lines from the processor bus areconnectable with the laboratory system C to provide an operator viewabledisplay showing the command signals, the shape and characteristics ofthe signals that are being sent to the nerves, and the like. Theappropriate stimulation electrical signal is conveyed through aninput-output port 98 to an output means 100. The output means 100includes a plurality of radio frequency transmitters in the preferredembodiment. In another embodiment, the output means applies the selectedstimulus signal directly to the electrodes through a percutaneousinterface.

A cable identification means 102 determines which cables areinterconnected with the portable unit. In the preferred embodiment. Theportable unit B serves as both an exercise system as well as afunctional system. Electrically induced exercise enables the musclestrength and fatigue resistance to be increased. In the exercise mode,the input command controller A is disconnected or disabled. In thepreferred embodiment, the exercise mode is selected without externalswitches by merely disconnecting the cable to the input commandcontroller and completing the connection with the implanted electrodes.The exercise algorithm allows the grasp to be ramped open, closed, andheld at particular values. Alternately, the exercise algorithm can cyclebetween two or more grasping patterns and turn on and off in a presettime cycle. A typical exercise regime, which is applied throughout thenight while the patient is sleeping, provides a 50 minute period ofalternating grasp modes and a 10 minute rest period.

A power management means 104 controls the power sources which power theportable unit. In particular, the power management means monitorswhether the portable unit is connected with line power, the level ofcharge in rechargeable batteries, and the presence of servicablebatteries. The power management system selects which of the availablepower sources are to be utilized. If rechargeable batteries and linepower are both available, the power management initiates the rechargingof the rechargeable batteries. If a power cable should be pulled out orif a battery should run down, the power management system automaticallychanges to another power supply.

A watchdog timer 106 monitors for system problems and shuts the portableunit off if a problem arises. In particular, the microprocessors cyclethrough the program at predictable intervals. The watchdog timermonitors the cycles and if a cycle fails to come in the appropriateperiod, a software problem is assumed and the system is shut off.

With reference to FIG. 8, the stimulus pulse train signal which isapplied to the electrodes E includes a series of biphasic pulses 110.Each pulse has a pulse width 112 and an amplitude 114. The leading edgesof adjacent pulses are separated by an interpulse interval 116. A shortinterpulse delay after each stimulus pulse, an opposite polarity pulse118 is applied to the electrodes. The delay prohibits repolarization ofthe active nerve fibers. The amplitude and duration of the oppositepolarity pulse are selected such that the net charge transfer of thereverse polarity pulse is some proportion of the stimulation pulse,usually zero. Zeroing the net charge transfer helps prevent tissuedamage with long term usage.

With reference to FIG. 9, the functional interrelationship of the partsof FIG. 7, particularly the function of the microprocessors and othersoftware are explained in greater detail. A selected motor functiondecoder 120 determines the selected motor function indicated by thefunction selection signal and enables one or more of a plurality ofelectrode stimulation signal parameter selection means or channels 122.For example, a selected motor function may require the stimulation of apreselected subset of the implanted electrodes. The selection of afreeze or hold function may be implemented by holding or freezing thecommand signal such that the signals controlling the positions of thepatient's hand or arm remain fixed.

In the preferred embodiment, each of the stimulation parameter selectionmeans or processing path is the same construction. Specifically, eachstimulation parameter selection means includes an amplitude algorithm124 which selects an appropriate amplitude 114 of the stimulation pulsein accordance with the proportional signal. In the preferred embodiment,the amplitude algorithm means 124 is a 1 byte×256 memory or look-uptable. Each of the 256 memory positions are preprogrammed to beretrieved by a corresponding one of 256 processed proportional signallevels. An amplitude index means 126 addresses the corresponding inputof the amplitude look-up table.

An interpulse interval algorithm means 128 including an interval indexmeans 130 provides an appropriate interpulse width for each level of theproportional signal. The interval algorithm means 128 is againpreferably a 1 byte×256 memory or look-up table. A pulse width algorithmmeans 132 including a pulse width index 134 select an appropriate pulsewidth 112 in correspondence with the proportional signal. The pulsewidth algorithm is again preferably a 1 byte×256 memory or look-uptable. The relationship between the proportional signal and the selectedamplitude, interpulse interval, and pulse width vary from patient topatient. Further, these relationships vary as the patient developsincreased muscle tone and strength through increased exercise of thestimulated muscles. Accordingly, the values in each of the look-upmemories are loaded and readjusted by the central control system C foreach patient and fine tuned for each patient periodically.

When the stimulation system D is implanted, the amplitude, interpulseinterval, and pulse width parameters are conveyed to a radio frequencyencoder 136 which encodes a radio frequency carrier signal with theselected electrode number, the amplitude, the interpulse interval, andthe pulse width information. The transmitter 100 transmits the encodedradio frequency signal to the implanted stimulator system D. In thepreferred embodiment, the radio frequency encoding scheme includes bothdigital and analog encoding. The electrode number is digitally encodedby periodically blanking the radio frequency signal to provide a digitalrepresentation of the electrode number to which the current is to beapplied. The amplitude is also encoded digitally. In the preferredembodiment, two digital pulse spaces provide an encoding scheme toselect one of 32 amplitude levels. The pulse width is encoded with ananalog encoding scheme in which the width of an off portion of the RFcarrier signal is indicative of the pulse width. The interpulse intervalis selected by the frequency or periodicity with which the parametersare transmitted. That is, the interpulse interval is controlled by thefrequency with which the RF carrier is encoded. If the stimulationpulses are channelled directly to the electrodes, the stimulus or apulse train generator D may be carried with the portable unit B. Thestimulus generator assembles a pulse train with the selected amplitude,interpulse interval, and pulse width.

The system may be operated in an open loop mode as described above.Alternately, closed loop operation may also be provided. A position ormovement monitor or transducer 140 monitors the movement, position, ordegree of extension or flextion of the limb or digit to be moved.Analogously, a force monitor or transducer 142 monitors the force withwhich the fingers or other limbs or digits are contracted or extended.It is to be appreciated that even the simplest limb movement involvesthe operation of two antagonistically operated muscles. A first muscleor group of muscles operates to move the skeleton in one direction whilea second muscle or group of muscles provides an antagonistic or counterforce. When the forces balance in three dimensions, the limb is heldstationary. When one force exceeds the other, the limb moves in thedirection of the predominant force vector. The stationary position ormotion is controlled by the difference between these antagonisticallyapplied forces. Although the relative forces applied by the antagonisticmuscles may be relatively high or relatively low, only the difference inthe forces is observed by the position or motion transducer.

With reference to FIG. 10, an exemplary position and force diagram ispresented for gripping an object between the thumb and the knuckle ofthe forefinger. The proportional signal starts at one extreme indicatingthe hand is fully open or extended, generally in a handshake position,on the left side of FIG. 10. As the proportional signal progresses tothe other extreme on the right side of FIG. 10, the position of thefingers contracts generally along curve 144. That is, the fingers startwith no flextion and progressively flex until a fist position is reachedat position 146. Thereafter, the fingers cease becoming more flexed. Thethumb starts fully raised or fully flexed. At a point 150, the thumbcommences becoming less flexed, i.e. approaches the forefinger. At apoint 152, the thumb contacts the forefinger and stops flexing. Theforce with which this thumb moves is illustrated by curve 154. In theillustrated embodiment, the thumb moves toward the forefinger withrelatively little force until the thumb and forefinger contact point156. Thereafter, the force is increased by causing the appropriatemuscle to contract more strongly until a maximum force or grip isreached at point 158. In the illustrated embodiment, the force withwhich the fingers contract is illustrated by curve 160. In theillustrated embodiment, the fingers contract with relatively littleforce until the thumb contacts the forefinger. Thereafter, the finger orsqueezing force is increased to a higher level. Other relationshipsbetween thumb and finger force and position may, analogously, beplotted. Similarly, relationships of position and force between thefingers and thumb when performing other functions or for other limbs maybe plotted.

With reference again to FIG. 9, in the closed loop system, a force andposition look-up table 162 is preprogrammed with the selectedrelationships between the proportional command level and various fingeror thumb positions and forces. For example, the look-up table 162 may beprogrammed in accordance with the graphs of FIG. 10. A force comparingmeans 164 and a position comparing means 166 compare the actual positionand force monitored by position and force monitors 140 and 142 with thepreselected position and force values retrieved from look-up table 162.A force index adjusting means 168 and a position difference indexadjusting means 170 adjust the index means 126, 130, and 134 of theactive channels until the difference between the selected and actualposition and forces are optimized. The position and force differenceadjusting means may simply step the appropriate index or indices up ordown as may be required to bring the actual and selected force orposition into coincidence. Alternately, programming logic may beprovided to bring the force or position into coincidence more precisely.For example, large differences and small differences may be programmedat different rates to prevent overshoot or oscillating about thepreselected position or force.

As yet another option, a sequence control means 172 may be provided forcausing a preselected sequence of muscular movement and forces. Forexample, the preselected forces and positions of FIG. 10 may beprogressively addressed out to the force and position comparing means164 and 166. The proportional signal may be used to control the rate atwhich the addressing out progresses. It is to be appreciated, that thesequence may be used with the open loop system as well as with theclosed loop system.

With reference to FIG. 11, the instrumentation and processing requiredfor functional neuromuscular stimulation orthoses can be separated intoseveral conceptual stages. A first stage 180 is to transduce and processcommands to provide parameters suitable for planning a desired movement.These parameters specify the type of movement to be executed as well asmovement parameters such as the magnitude or velocity. The first stageof processing may range from simple gain or offset changes to accessingtransformations, signal filtering, and quantitization of continuouscommands.

A second stage 182 is the planning of movement based on the controlparameters. The second stage specifies the joint angle trajectories andapplied torques. These movement parameters are used by a third stage 184which coordinates and regulates the process to specify the stimulusparameters to be applied by the stimulus generator D to the muscles.

If a closed loop control sequence is implemented, a force and positionmonitoring stage 186 monitors the forces and positions achieved by theuser. A feedback stage 188 converts the sensed force and positioninformation into a map of actual physical movement for comparison withthe planned movement parameters. Deviations between magnitude ofmovement, velocity of movement, trajectory, end position, and othermovement parameters are used to adjust the planned movement parametersand the stimulus.

With reference to FIG. 12, the hardware for the laboratory system Cincludes a central processing unit 190. An analog to digital converter192 converts the analog output of potentiometers 194 of a joystick, suchas the joystick of the input control means A to digits. Thepotentiometers 194 may be attached to the patient or may be available tothe operator. For example, the amplitude of the stimulus pulses can beset manually by the operator on potentiometers 194. Force and positionmonitoring transducers 156 also produce analog output signals indicativeof patient motion and force. The position and force analog signals areconverted with the analog to digital converter 192 and a digital inputmeans 198 to an appropriate input for the central processing unit.

A digital output device 200, a microprocessor based pulse width andinterpulse interval modulator 202, and output stages 204 provide abiphasic current pulse train to the electrodes to stimulate the patient.The stimulus pulse train, as illustrated in FIG. 8, has a rectangularcathodic phase followed by an anodic phase generated by capacitivedischarge through the tissue. An interphase delay on the order of of 0to 100 microseconds between cathodic and anodic phases has been found tobe a value which allows an action potential to develop but which reducespotential tissue damage. If the delay between the two phases is toosmall, the nerve may repolarize prior to developing an action potential.If the delay is too long, the biproducts and discharge transfer at theelectrode surface may diffuse away from the electrode. The biphasicstimulus insures charged neutrality for minimal tissue damage.

The microprocessor based modulator 202 stores stimulus informationdescriptive of the stimulus to be applied to the electrodes. The samestimulus or pattern is repeatedly applied to the electrodes until thecentral processing unit 190 reprograms the modulator memories. In thismanner, only changes need be communicated to the modulator. Morespecific to the preferred embodiment, the modulator allows the flexibleformation of stimulus groups, i.e. one or more stimulus channels thatoperate at the same interpulse interval. The modulator stores the numberof stimulus groups within the stimulation system, the stimulus channelsbelonging to each group, the interpulse interval for each stimulusgroup, and the stimulus pulse duration for each stimulus channel. Inthis manner, stimulus pulse trains may be applied by each electrode at afaster rate than would otherwise be permitted by the speed of thecentral processing unit.

The pulse width, current amplitude, and the interpulse intervalmodulation can be controlled independently for each electrode. Thisallows modulation of the muscle force by recruitment (pulse width oramplitude) and by temporal summation (interpulse interval). In apreferred intramuscular stimulation embodiment, pulse widths on theorder of 0 to 255 microseconds may be selected with a resolution of onemicrosecond. For other applications such as direct nerve stimulation,surface stimulation, and the like, other appropriate pulse widthsranges, interpulse intervals, amplitudes, and resolutions may beselected. The stimulus timing is controlled by the software which isdiscussed below.

Other peripheral hardware includes a feedback generator 206 forproviding audio, electrocutaneous, or other feedback to the patientregarding the operation of the system, e.g. whether the system isactive, etc. A digital plotter 208 and a printer 210 provide a hard copyof the data and parameters. A graphics storage oscilloscope 212 and avideo terminal 214 provide the operator with appropriate information,such as stimulus signal strength and parameters, patient position andresponse, system functioning and parameters, and the like.

The software provides the intelligent decision making capability of thestimulation system. The software may be divided into four main sections.The first section provides the operator with methods to examine andspecify the operation and configuration of the system. The remainingthree sections are real time processes that convert the input commandsignals to control parameters, process the control parameters to specifystimulus parameters, and activate the external hardware to generate thestimuli. The operator interaction system is streamlined for ease of usewith many different uses or subjects. The operator may specify thechannels of stimulation. The stimulation channels may be organized intogroups for sequential stimulation. Channels within a group are activatedin a fixed sequence. For a constant interpulse interval, the phasing ofone channel with respect to the next may be determined by dividing 360°by the number of channels in the group. Optionally, the channels mayhave selected non-uniform relative phases. The group organization alsoallows sequential stimulation in which portions of single muscle ormuscle synergists are activated at a low frequency, out of phase witheach other. Because the forces ellicited by the individual channels sumat a joint, a fused response can be maintained at a lower stimulusfrequency on each channel than would be possible with a single channelscheme. This reduces fatigue. Channels may also be activatedpseudo-simultaneously by putting them in separate groups with the sameinput control signal and the same relationship between the controlsignal and the interpulse interval.

The relationship between the control signals and the stimulus parametersmay be specified for each channel. The system allows a non-linear pulsewidth and interpulse interval modulation to correct for non-linearmodulation of muscle force by recruitment. Piecewise linearrelationships can be specified between a single continuous controlsignal and the interpulse interval and the pulse width of each channel.The coordination of different muscles is achieved by specifying stimulusmodulation of stimulus parameters in different channels by the samecontrol signal.

The piecewise linear relationships may be specified by the end points ofindividual linear segments. These end points can also be specified oraltered while stimulation is taking place by assigning the control ofthe individual channels to specific potentiometers on the analog todigital interface. A separate command channel can control the interpulseinterval modulation and another command signal can be assigned tocontrol pulse width modulation for each channel. One or more channelscan be controlled independently of the others so that its contributionto the coordinated movement can be assessed or altered. When thestimulus parameters for that channel are appropriate, as assessed byvisual monitoring or measurement of the movement or force, thatcombination of stimulus parameters can be entered automatically as oneof the end points of a linear segment.

Command input information, stimulus parameters, patient information,data about the test and muscle being stimulated, electrode information,and general comments can be entered and stored in a secondary storagemedium 216. This enables the system to be used as a notebook. Thenotebook information may be printed out or recalled automatically tofacilitate set up in subsequent tests with the same patient.

The operator can display graphically the relationships between thecommand signals and the stimulus parameters in several ways. Theserelationships can be plotted on the storage graphics oscilloscope 212 orplotted as hard copy on the digital plotter 208. A less detailed displayis available continuously on the video terminal 214. The range of pulsewidth and interpulse interval modulation is displayed as a function ofthe command input for each channel. This display allows the operator tosee the relationship between pulse width and interpulse intervalmodulation on one channel as well as with respect to other channels.This information enables the operator to assess which muscles arecoactivated.

With reference again to FIG. 11, the command processing section 180 ofthe software is a real time process which converts one or more inputcommand sources into control parameters. The purpose of this process isto translate external command signals from their raw form into aninternal digital parameter suitable for specifying stimulus parameters.The command processor has been designed to accept one or more analoginput signals as the command storage. Accordingly, most any commandsource may be made compatible with the system. Suitable command sourcesinclude joint positions, myoelectric signals, or contact information.

The assignment of command inputs to the control of the individualchannels or groups of channels can be accomplished as described above.However, more accurate inputs can be obtained than the command input asreceived from the transducer 196. The processing provided by thissection of the program converts the information to the proper form.Several operations may be performed on the input command. The processingof the preferred embodiment converts command information derived fromthe shoulder position of the patient obtained from transducingelevation-depression and protraction-retraction movements of thepatient. The position command of one axis is used as the proportionalcontrol parameter and the velocity movement of an orthogonal axis isused to initiate a logic function. First, the program provides atransformation for linearizing the output of the transducer byprojecting its spherical image into x,y coordinates.

The signal is further processed to translate the transducer axes intoperceived patient axes. This allows for compensation for the patient'sactual shoulder movements and also may allow for the use of axes whichare not truly orthogonal. The signal is scaled to match the full rangeof the patient's shoulder movement to the internal control parameters inorder to maximize resolution in the command process. Re-zeroing ornulling specifies an arbitrary level of a command that the patient wantsto use as a reference for movement. This allows the patient to selectany value in the command range as the null or zero point. In thesubsequent section of the program, this null point may be set tocorrespond to a specific point in the range of control parameters. Forexample, the null point may be set to correspond to the middle of thecontrol parameter range so that movements in one direction can be usedto perform a function different from movements in the oppositedirection.

Hold processing enables the present control parameter level to bemaintained despite subsequent changes in the command on the proportionalaxis. In the preferred embodiment, the velocity on the logic axis iscompared with a preselected level to determine whether the controloutput should be held at a constant value. In this manner, the patientmay move his shoulder suddenly to initiate the constant value mode. Thepatient may regain control by again exceeding the velocity threshold andreturning command to the proportional command axis. A time delay in theproportional axis creates a lag between the logical axis and theproportional axis to insure that inadvertent movement does not alter thecontrol output of the proportional axis prior to the hold command. Thetime delay is a software adjustable parameter which is a function of theability of the subject to separate the proportional control axismovements and the logical signal axis movements from one another.

The movement planning and coordination section 182 translates thecontrol parameter(s) that is produced by the command processor into aset of stimulus parameters that correspond to each control parameterlevel. The piece-wise linear modulation process is simplified by the useof look-up tables. In the preferred embodiment, the input controlparameter is treated as having eight bit resolution and one 256-elementinteger array as allocated for the pulse width modulation for eachchannel and one 256-element interger array as allocated for theinterpulse interval modulation of each group. The contents of each pulsearray are filled during the parameter setting procedure and the valuesare loaded into the microprocessor based modulator to produce a desiredpulse width corresponding to each possible value of the command. Thecontents of each interpulse interval array are the actual interpulseintervals to be set to the stimulus timing process of the stimulusgenerator D. The contents of these arrays, when finally adjusted, areloaded in the look-up table 124, 128, and 132 of the portable unit B.

The movement coordination and regulation process 184 runs in acontinuous loop which runs whenever the command process and stimulustiming process are not being serviced. Each time through the loop, theinput control signal level is used as an index to the look-up table foreach of the channels and groups in use. The contents of the pulse widthlook-up tables at that entry are then loaded into the microprocessorbased modulator. The movement planning and coordination process alsochecks for instructions that are entered at the terminal by the operatorand updates the display of stimulus parameters on the terminal.

The fourth or stimulus processing stage controls the stimulus timing foreach of the groups. The timing can be communicated to the electrodeseither with an implanted stimulator or a percutaneous system implementedwith output stage modules. Communication of stimulus information fromthe computer is carried over a parallel interface. One or more stimuluschannels are provided, each of which operate at the same interpulseinterval. The coordination and regulation stage 184 indicates theelectrodes which are within each stimulus group, the channels whichbelong to each group, the interpulse interval for each group, and thestimulus pulse durations for each channel. The stimulus generator stagestores the received information and repeatedly stimulates the electrodesin accordance with the stored information. The coordination andregulation stage 184 as necessary changes the stored information tochange the stimulation parameters. Stimulus information is updated asneeded, allowing complete modulation of all group interpulse intervalsand individual channel stimulus pulse durations.

With reference to FIGS. 6 and 13, the software creates a model of theposition and force for a selected movement and sets appropriate stimuli.As the patient practices the motion, the patient's muscle tone improvesand the response of the muscles to a given stimuli changes. To this end,the laboratory system is periodically used to adjust the portable systemof the patient for desired performance. A function selection means 220selects an appropriate motion of the patient to be fine tuned. A motionmodule 222 selects the appropriate force and position for each musclewhile performing the movement, as shown for example in FIG. 13. Astimulus selection means 224 formats an appropriate stimulus to achievethe selected motion. In particular, the stimulus selection means 224selects the amplitude, interpulse interval, and pulse width to be storedin the portable, patient carried unit B. A stimulus generator D appliesthe selected stimulation pulse train.

The actual position and force achieved by the patient as the movement ismonitored by empirical observation or by a position monitor 228 and aforce monitor 230. A comparing means 232 compares the actual positionand force from the monitors with the select position and force from themotion model module 222. Any differences between the position and forcealter the selected stimulus pulse train parameters accordingly. Thisprocess is iteratively repeated readjusting the control algorithms untilan optimum match is achieved. The reoptimized control algorithms areloaded by the microprocessor based stimulus selecting means 224 into thecontrol algorithm memory 60 of the portable unit B. This matchreoptimize is repeated periodically to maintain the patient operating atthe best possible mode.

With reference to FIG. 14, a preferred upper body control input commandto control processing schemes is illustrated. The command input means Ais mounted to the patient and connected with the laboratory unit. As thepatient moves his shoulder or other portion of the anatomy to which theinput command means is attached, an axis resolving means 240 determinesand resolves the proportional instruction axis and the functionselection or logic axis. As described above, it is advantageous toselect the proportional control along an axis over which the patient hasrelatively large and relatively accurately controllable range of motion.Because the logic or function selections are carried out in thepreferred embodiment by sudden movements, it is advantageous to selectthe function or logic selection axis as one over which the patient canmove his shoulder rapidly a significant distance. As also indicatedabove, it is advantageous for the axes to be othogonal to avoidcross-talk. However, limited amounts of cross-talk may be satisfactorilyremoved with appropriate filtering, signal analysis, and the like.

A range of movement measuring means or step 242 measures the patient'srange of movement along the proportional axes resolved by the axesresolving means 240. A filter selecting means or step 244 monitors thesmoothness or degree of accuracy with which the patient moves along theproportional axis. A filter function is selected which removesunevenness or lack of coordination or control by the patient as he movesalong the proportional axis. An amplitude selection means or step 246selects an appropriate output signal amplitude for each position alongthe range. The amplitudes are selected in the preferred embodiment toprovide a linear relationship between the output and motion. However,other relationships may be provided as is appropriate. For example, forsome applications, it may be advantageous to have more precise controlat one end of the range. To achieve more precise control, a greaterrange of movement may be required for a corresponding change in thesignal.

A velocity and time measuring means or step 248 measures the velocityand duration over which the patient can move his shoulder along thelogic axis. A filter selection means or step 250 selects an appropriatefilter to remove incidental movements which are smaller than the readilyobtained velocity and time movements in order to inhibit false signals.An amplitude selecting means or step 252 selects appropriate on/offamplitudes to indicate that the patient has selected a change in thecommand function. Again, the amplitude and filter functions areperiodically re-evaluated as the patient becomes more adept. Theselected amplification, velocity threshold and axes, and the like arerecorded in the portable patient carried system B.

With reference to FIG. 15, the data collection/system evaluation portionof the system determines whether the system is working properly and ifnot, diagnoses what is wrong. A diagnostic algorithm 260 monitors andcompares the input command signals from the input means A with themeasured position and force of the patient. When the two becomeinconsistent, an appropriate diagnostic correction is determined fordisplay on the printer 210 or video terminal 214. For example, thediagnostic algorithm looks for intermittent, large differences betweenthe measured and commanded positions and forces. As another example, thediagnostic algorithm looks for a gradual shift in the two over timewhich would be indicative of muscle tone improvements by the patientwhich show that recalibration is required.

An electrode impedence monitoring means or step 262 monitors theimpedence across each electrode. Changes in the wave form of theimpedence are indicative of system failures. For example, a sudden jumpin the impedence may indicate a break in the electrode or lead wiresthereto.

With reference again to FIG. 13, a memory means 270 periodically storesthe differences between the motion model and the actual motion and forceachieved. An improvement algorithm 272 analyses the differences storedover a long period of time to determine whether the patient is becomingmore proficient. The improvement algorithm determines monitoring whetherthe patient and the system are able to work together to achieverepeatable and stable results. The improvement algorithm determines fromthis information whether the system needs adjustments and refinementsand how well the patient is performing over time.

With further reference to FIGS. 6 and 12, the central processing unit190 further performs motoric and neurological assessment procedures.These procedures determine whether a person is a candidate for theprogram. In this procedure, an analysis of the nerves which are stillintact and functioning in the affected limb to be controlled aredetermined. Surface stimulation is applied to cooberate which nerves areintact. The range of motion over which the limb can be articulated aremeasured and evaluated. A sensory evaluation determines the extent ofsensory feedback or feeling in the limb. Commonly, patients with adamaged spinal column are spared the loss of some sensation in the limbproviding the patient with a limited amount of feedback. This systemalso determines the level of voluntary control of musculature. That is,it is determined how much the patient can do compared to a scale of anormal individual. The laboratory system evaluates this data anddetermines whether or not the patient is a likely candidate for thepresent invention.

With reference to FIG. 16, the implantable stimulator D includes anelectronic circuit 290 which receives and decodes incoming stimulusinformation, provides output stimulus pulses to the electrodes, providesimmunity from external disturbances, and maintains safe operatingconditions. The electronic circuitry is packaged in a hermeticencapsulation constructed of biocompatible materials. The physical sizeof the packaging and the electronic circuitry is minimized to increasethe flexibility in selecting implantation sites in the patient. Thestimulus electrodes E each include a narrow, flexible conductive lead292 for conducting the stimulus pulse train from the implantedelectronics to the appropriate muscle group. A terminal stimuluselectrode 294 provides direct tissue interface to the muscles forstimulus charged injection and subsequent charge recovery. A referenceelectrode 256 completes the circuit.

With particular reference to FIGS. 16 and 17, the implanted stimulatorobtains its electromotive power through radio frequency electromagneticinduction. In particular, the stimulus signal parameters are encoded ona 10 MHz radio frequency carrier. A receiving coil 300 is connected,analogous to a secondary coil of a transformer, with a full waverectifier 302, a voltage limiting zener diode 304, a filtering capacitor306, and a voltage regulator 308.

Because the efficiency of power transmission through the patient's skinis only about 30%, the power consumption requirements of the implantedcircuitry are kept to a minimum. To minimize the power consumption, thecircuitry 290 utilizes CMOS technology. Further, the CMOS circuitry iscustom designed to achieve high density integration with a relativelysmall number of system components. This results in versatile circuitdesign with high reliability, a reduced number of fabricationprocedures, and a small circuit size.

As set forth above, the modulation of the carrier pulse in the preferredembodiment is achieved by gating the carrier frequency on and off.Optionally, other conventional frequency and amplitude modulationtechniques may be utilized. The control signal includes two parts, adigitally encoded portion and an analog encoded portion. Optionally, alldigital and all analog coding schemes may be advantageously implemented.The digitally encoded portion carries a digital indication of which theelectrode channel is to carry pulses in accordance therewith. Theamplitude of the pulses is also digitally encoded. In the preferredembodiment, the pulse width is encoded with an analog encoding scheme inwhich the width of an off portion of the RF carrier signal is indicativeof the pulse width. The frequency with which the modulated pulse packetsare transmitted is indicative of the interpulse interval. In thismanner, channel selection, stimulus pulse width, stimulus pulseamplitude, and stimulus pulse interpulse interval are all under externalcontrol.

A control signal recovery means 310 separates the coding pulses from thecarrier signal. The digital channel number encoding is decoded by achannel decoder 312. The digital amplitude designation is decoded by anamplitude decoding means 314. The pulse width encoding is decoded with apulse width decoder 316. An interpulse interval decoder 318 sets theinterpulse interval. With the interpulse interval encoded in therepetition frequency of the control signal, the interpulse intervaldecoder may be a trigger circuit for triggering a new stimulus pulse inresponse to a preselected portion of the signal. The channel selection,amplitude, pulse width, and interpulse interval decoders are connectedwith an output stage 320 which creates a stimulus pulse train of theselected characteristics on the selected channel.

A voltage monitor 322 monitors the voltage of the power supply anddisables the logic circuitry if the voltage should fall below apreselected level. The low voltage may be due to various factors such asantenna misalignment or low transmitted power. When the voltage returnsto the preselected level, the voltage monitor 322 again enables thelogic circuitry.

The power supply includes an energy storage means 330 which storespotential for applying current pulses to electrodes in each channel.Because a current pulse is transmitted for a relatively short durationof each cycle, the charge may be accumulated during the non-tramsmittingportions of each cycle. The charge from the energy storage means 330 isselectively conveyed to the electrodes 294 by a channel selectionsection 332. Current flows from the electrodes 294 to the groundedreference anode 296. A switch 334 is closed when no current is flowingbetween the electrodes to recharge the energy storage means 330 and isopened by the output circuit 320 during current discharge across theelectrodes.

With particular reference to FIG. 18, each of the output stages providesa regulated current output for the excitation of muscle tissue followedby a current reversal to recover injected charge necessary to minimizetissue damage. During stimulation, the output circuit 320 provides astimulus pulse to the base of a switching transistor 340 in the channelselection means 332. When the transistor turns on, a stimulus current342 flows from an energy storage capacitor 344 through the collector tothe emitter controlled by a stimulus current regulator 346 and throughthe muscle tissue between the electrodes. The stimulus current regulatoris set by the output circuit 320 to provide the selected one of aplurality of current amplitudes. For example, a typical amplitude may be20 milliamps drawn from the capacitor 344 of the energy storage device330. The stimulus pulse occurs concurrently with the duration of thecontrol command, i.e. the pulse width. At the end of the stimulus pulse,the transistor 340 is turned off, halting the stimulus current. Thecharge storage capacitor 344 now recharges back up to the power supplyvoltage. A recharging current flows through the switch 334, an isolationdiode 348, and a charge regulator 350 and a reverse current 352 flows inthe reverse direction from the stimulus electrode 294 to the anode 296providing the charge recovery and completing the biphasic stimuluspulse.

The output capacitor 344 serves three functions. First, it provides areservoir of energy from which relatively large currents can be drawnfor short periods of time. Second, it provides a charge reversal andinsures complete charge recovery. Third, it provides AC coupling for thestimulating electrode blocking DC current flow between the stimulatingelectrode and anode whether the circuit is active or dormant. The DCcurrent blocking coupled with a maximum capacitor leakage current of 1microamp helps prevent possible galvanic electrochemical corrosion whendissimilar metals are used for the stimulus electrodes and the anode.

Recharging current to the energy storage capacitors is limited to 0.5milliamps for two reasons. First, it places only a relatively smalldemand on the RF power circuit, even when several channels arerecharging simultaneously. Second, during recharge current direction issuch that the stimulating electrode would undergo anodic electrochemicalcorrosion. The low level of the recharge current helps prevent thepotential delivered to the electrode during the anodic phase fromexceeding the potential at which the electrode materials may corrode.

A zener diode 354 on the base of the switching transistor 340 preventserroneous stimulus output during powering up and powering down of thestimulator circuitry. During removal or replacement of the externalpowering antenna, the integrity of the control logic cannot beguaranteed as the logic supply voltage rises and falls. The zener diodeprevents transistor switching until the control logic is stable.

With reference again to FIG. 16, the stimulus current regulator 346operates on a current mirroring principle. One of a plurality ofselectable reference currents is set up using one of a plurality ofreference mirror CMOS transistors 360. Due to the uniformity of devicecharacteristics on the same integrated circuit die, this reference canbe used to mirror the reference current into other discrete mirrorcurrent transistors 362. By selectively grouping different numbers andgeometry types of the current mirror transistors together with eachreference mirror transistor, one can select a regulated current that isone of a wide range of multiples of the reference current. Byselectively gating different numbers of the mirror transistorsconductive, different amplitudes of the stimulus currents may beselected. In the preferred embodiment, stimulus currents in the range of0 to 32 milliamps may be selected. To conserve power, the referencecurrent is applied to reference mirror transistors 360 only during theoutput of a stimulus pulse. If all of the output stages share the use ofthe same current regulator, simultaneous outputs from two or more of thechannels may not be obtained at their full amplitude.

When using the portable system to control a plurality of implantedstimulators, an interrogation system 370 is provided to enable theportable unit to ascertain which implanted stimulator is interconnectedwith each transmitting coil or aerial. On initial set up, the portableunit interrogates the implanted stimulator which is interconnected witheach transmitting coil and receives an implanted stimulator indicatingsignal back. The portable unit switches the appropriate control circuitsfor each implanted stimulator into interconnection with the appropriatetransmitting coil.

In the preferred embodiment, the implanted stimulator interrogationsystem includes an identification signal decoder 372 which decodes acommand for the implanted stimulator to identify itself. In response toreceiving the appropriate code, the decoder closes a switch 374 to placea load 376 having a unique characteristic across the receiving antenna300 for a preselected duration. The load produces an observable changein the transmitter characteristics, which observable change isindicative of the implanted stimulator.

Again, the RF powering of the implanted device is accomplished byexciting the transmitting coil of a loosely coupledtransmitting/receiving coil pair with an RF signal. The electricalproperties of the transmitting coil are dependent primarily on thegeometry and construction of the transmitting coil and secondarily theeffect of coupling the receiving coil into the field generated by thetransmitting coil. The degree of the effect on the transmitting coildepends on the factors that affect the secondary/receiving coil. Thesefactors include the geometry of the receiving coil, the orientation ofthe receiving coil in the transmitted field, and the changes ofelectrical activity in the receiving coil circuit. In the preferredembodiment, it is the changes in the electrical activity in thereceiving coil that are altered by switching the characteristic loadthereacross. Optionally, the self resonant frequency of the coil mayalso be changed. Changing either the load or current in the receivingcoil or the self resonant frequency of the receiving coil causes acorresponding change in the impediance of the transmitting coil. Thechange in impediance can be monitored in the portable unit as a changein voltage amplitude across the transmitting coil which is readilymonitored by a conventional voltage amplitude monitoring circuit.

Other implanted stimulator identification mechanisms may be optionallyutilized. As one example, the load may be connected continuously acrossthe receiving coil. As another example, the switch 374 may be opened andclosed in a characteristic pattern to provide a digital or otheridentification signal.

With reference to FIG. 19, each implanted stimulator D is encapsulatedin a sealed, implantable capsule assembly. An electronic componentreceiving capsule 380 is machined from solid titanium stock. The capsulehas an inert gas filled internal cavity of appropriate dimension toreceive the electronic circuitry 290. A titanium lid 382 is hermeticallysealed to the capsule and has an exposed surface to function as ananode. At one end, the capsule defines a recess 384 with three aperturestherein. The apertures receive feedthrough assemblies 386 for feedingthe three leads of the receiving coil 300 into the capsule forinterconnection with the electric circuit 290. In the preferredembodiment, the feed through assemblies include a non-corrosive, metalconductive pin 386 which is encased in a ceramic plug 390. The recess384 is defined by overhanging capsule portions to protect theinterconnection between the coil and the feed-through assemblies.

At the opposite end, the capsule defines another recessed cavity 392 anda plurality of apertures extending into the capsule internal cavity. Thenumber of apertures corresponds with the number of electrodes which areto be controlled. Feed through assemblies 394 provide an electricalinterconnection between the circuit 290 and lead wires 396 eachextending to one of the electrodes.

The antenna 300, the capsule recess cavities 384 and 396, and portionsof the feed through assemblies 386 and 394 are encapsulated in an epoxylayer 398. A biocompatible elastomeric sealant layer 400 encloses theepoxy and the titanium capsule except for the portion of the lid whichfunctions as an anode. A resilient strain relief mounting means 402protects the electrode wires 396 from mechanical failure adjacent thecapsule. A woven dacron apron 404 is connected with the capsule toenable the capsule to become anchored into the tissue of the patient.

With particular reference to FIG. 20, the electrode leads 196 include acolor encoded center strand or former 410 about which first and secondmulti-strand wires 412, 414 are wrapped helically. In the preferredembodiment, each wire includes a plurality of stainless steel strandswhich are encased in a TEFLON coating. Interstices between the wirehelixes are filled with a transparent elastomeric insulator 416. Atransparent, elastomeric tube 418 surrounds the spiral wrapped wires.

With reference to FIG. 21, one lead is permanently connected with theimplanted module D and another lead is permanently connected with one ofthe implanted electrodes E. An interconnection 420 interconnects thelead from the electrode with the corresponding lead from the implantedmodule. This facilitates installation of the electrodes, implantedmodule, and leads within the patient and the replacement of electrodesshould one become damaged, dislodged, or otherwise unservicable. Eachlead includes a connector portion 422 of like construction. Eachconnector portion includes a conductive pin 424 which is electricallyconnected with the multi-strand wires of the lead. In the preferredembodiment, the pin is hollow and has a cut-out portion 426 tofacilitate access to the multi-strand wires to weld them to theconductive sleeve. An elastomeric support 428 encases a portion of thepin 424 and a cord spring 430 which abuts a beveled end of the pin toprovide strain relief between the pin and the lead 396. A conductivecoil 432 is dimensioned to be received in tight frictional engagementwith the conductive sleeve or pin 424 of each of the connectors.Pressing the connectors together tends to expand the coil 432 enablingthe pins to be nore readily received. Separation of the connectorscauses tension on the spring which contracts its diameter causing it toadhere more strongly to the pins. In this manner, a secure, yetflexible, connection between the connectors is provided. An elastomericsleeve 434 is secured by sutures 436 and 438 adjacent opposite terminalends of the connectors to provide a seal which prevents body fluids fromcoming into contact with the electrical interconnection.

FIGS. 22 and 23 illustrate an alternate embodiment of a patient inputdevice A. Like the Hall effect input device illustrated in FIGS. 1, 3,4, and 5, the input device of FIGS. 22 and 23 may be implanted ormounted externally, with the external mounting being preferred. A socketportion 450 is mounted to one portion of the patient's body. A sensingarm 452 is mounted to another portion of the patient's body which hasretained voluntary muscular control relative to the portion of the bodyto which the socket 450 is attached. The sensing arm is connected with aferrite core 454 which is mounted in a ball member 456. The ball memberis rotatably received in the socket 450 such that the sensing arm isfree to move with two degrees of freedom.

In the preferred embodiment, a driver coil 460 surrounds the socket 450,a portion of the ball member 456, and a significant portion of theferrite core 454. Four sensing coils 462, 464, 466, and 468 are mountedin the socket member 450 closely adjacent the ferrite core. A highfrequency input signal applied to the driver coil 460 is transferredthrough the ferrite core 454 to the sensing coils 462-468. The relativepercentage of signal transfer to each of the sensing coils varies inaccordance with the proximity of the ferrite core thereto.

With reference to FIG. 24, the portable patient carried system C may beused with a direct electrical connection to the electrodes E. Such adirect connection requires electrical leads to pass from the exteriorportable unit through the patient's skin to the implanted electrodes.Although the patient's skin will heal and grow up to the electricalleads, a passage is defined between the skin and the leads. As with anypercutaneous structure, bacteria or foreign antibodies may invade thelimb through this passage causing deep abcess, granuloma, or contactdermititis. Common clinical procedures for percutaneous structuresinclude applying and changing dressings regularly.

A percutaneous interface structure is provided which facilitatescleansing the area of the limb around the electrode leads, whichprotects the lead wires from damage and catching and which protects thepatient against catching the lead wires and pulling or ripping theelectrodes from the implantation site. The electrodes E are connectedwith lead wires 292 which pass through the skin at a site 470 and whichare interconnected with a multichannel electrical connector 472. Theelectrode lead electrical connector 472 is configured for selectiveinterconnection and disconnection from a mating shield mountedelectrical connector 474.

The shield mounted connector 474 is surrounded with an elastomericprotective shield member 476. The protective shield defines an aperture478 surrounding the site 470. A receptacle receiving passage 480 extendsfrom the aperture to the electrical connector 474. The passage 480 isconfigured to receive the connector 472 in sufficiently firm frictionalengagement to render decoupling of the electrical connectors 472, 474difficult, yet with sufficiently little frictional engagement that theconnectors will decouple before the electrodes are ripped loose from themuscle tissue or other physical damage occurs. A lower surface of thepassage 480 is defined by a layer 482 of the resilient material whichfunctions as a pad or shock absorbing structure.

The shield member 476 is releasably adhered to the patient's skin suchas with a layer of double stick medical adhesive tape 490, or the like.To assist in preventing decoupling, the shield member has a low profileto decrease its chances for impacting nearby structures. Further, theshield member defines a relatively flat peripheral lip 492 which tapersupward gradually from the surface of the skin. Adjacent the center, acentral portion 494 projects upward from the lip with smooth roundededges. With this configuration, any impact to the shield structure islikely to be deflected as a glancing blow which will not separate orshift the shield member relative to the patient's skin. For greatersecurity, an overlayer of a flexible, porous medical adhesive 496 isadhered over the shield member. The overlay has an aperture 498 thereinwhich conforms to the inner edge of the lip portion 492 such that thelip portion of the shield member is overlaid by the overlay member. Theoverlay member extends a significant distance outward beyond the lipmember to provide a more secure bond with the patient's skin.

The electrical connector 474 in the preferred embodiment is a two sidedconnected and has a mating interconnection for a plug 500 which isinterconnected with the lead wires from the portable unit C. The shieldmember defines a second passage 502 for receiving the portable unitconnector 500 therethrough. In the preferred embodiment, the connectors474 and 500 mate in a plug and socket type relationship. The plug andsocket members of the connectors engage in a frictional relationship andthe body of plug member 500 engages in a frictional relationship withthe passage 502. The frictional relationships are selected such that theconnectors become disconnected under a force which is less than theforce required to move the shield member 476 relative to the patient'sskin, yet hold the connectors in firm electrical interconnection atlower interaction forces.

The invention has been described with reference to the preferredembodiment. Obviously, alterations and modifications will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such alterations and modifications in so far as they come within thescope of the appended claims or the equivalents thereof.

Having thus described the preferred embodiments, the invention is nowclaimed to be:
 1. An apparatus for providing electrical stimulationpulse trains of selectable parameters to electrodes which are implantedin muscle tissue, the apparatus comprising:an antenna for receiving aninput signal which includes a carrier frequency modulated with encodedstimulus pulse train parameters; an energy converting means forconverting energy from the carrier frequency into electrical potential;a decoding means connected with the antenna for decoding the encodedstimulus pulse train parameters from the received modulated inputsignal, said encoded stimulus pulse train parameters including at leastan indication of which electrode is to apply the stimulus pulse train, apulse width of the pulses of the pulses of the pulse train, and anamplitude of the pulses of the pulse train; for each electrode, aseparate electrical energy storage means connected with the energyconverting means for receiving and storing electrical energy obtainedfrom the carrier frequency by the energy converting means, the storedelectrical energy being sufficient to produce a biphasic pulse tostimulate said muscle tissue; and for each electrode, a stimulus pulsemeans, connected with a respective electrical energy storage means forreceiving the stored electrical energy therefrom and with the decodingmeans for receiving pulse train parameters therefrom, for selectivelypassing pulses of the electrical potential to the selected stimuluselectrode with at least the selected pulse width and amplitude.
 2. Amethod of providing electrical stimulation pulse trains of selectableparameters to electrodes which are implanted in muscle tissue, themethod comprising:receiving an input signal which includes a carrierfrequency modulated with encoded stimulus pulse train parameters;converting energy only from the carrier frequency into an electricaloperating potential; decoding the encoded stimulus pulse trainparameters from the received modulated input signal, the decodingincluding decoding at least an indication of which electrode is to applythe stimulus pulse train, and an amplitude of the pulses of the pulsetrain; for each electrode, separately storing a quantity of electricalenergy from the electrical operating potential, said quantity beingsufficient to produce a biphasic pulse to stimulate said muscle tissue;selectively passing pulses of electrical current from the separatelystored quantity of electrical energy between the selected stimuluselectrode and a reference electrode with the selected pulse width; andregulating the amplitude of the stimulus pulses in accordance with thedecoded amplitude.